Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$152.69	8.616%	$165.8458	$165.85	$165.85	$165.80
Purchase #2	$100.67	4.746%	$105.4478	$105.45	$105.45	$105.40
Purchase #3	$96.41	13.195%	$109.1313	$109.13	$109.15	$109.10
Purchase #4	$5.61	5.765%	$5.9334	$5.93	$5.95	$5.90
Purchase #5	$100.99	5.269%	$106.3112	$106.31	$106.30	$106.30
Purchase #6	$29.91	12.799%	$33.7382	$33.74	$33.75	$33.70
Purchase #7	$154.38	10.393%	$170.4247	$170.42	$170.40	$170.40
7 purchase totals =	$640.66		$696.8324	$696.83	$696.85	$696.60